In a case where organic pollution of sample solution such as a liquid containing few impurities, called pure water or ultrapure water, water for medicine manufacture, or process water for semiconductor manufacture is evaluated, carbon dioxide dissolved in such sample solution needs to be removed. In general, a gas component such as carbon dioxide contained in a liquid sample is removed by vacuum degassing or bubbling with nitrogen gas or the like before the liquid sample is introduced into an analyzer.
However, in the case of degassing by bubbling, bubbles are formed in a liquid sample, and therefore, when the liquid sample containing bubbles is introduced into a micro flow channel of an analyzer or a reactor, bubbles are trapped in a part of the flow channel and cannot be easily removed. Further, in a case where bubbles are introduced into an ultraviolet absorption detector of a measuring apparatus, abnormal noises are generated by the bubbles, and in a case where bubbles are introduced into an electrical conductivity detector of a measuring apparatus, the electrical conductivity of a liquid sample cannot be accurately measured. Further, in a case where bubbles are introduced into a part of a reactor where mixing of a reaction solution or synthesis is carried out, the bubbles adversely affect the flow of the reaction solution, and therefore, mixing of the reaction solution cannot be stably carried out, thereby deteriorating reproducibility.
Even when bubbling is not carried out, there is a case where noises are generated by bubbles originally contained in a liquid sample. For this reason, bubbles contained in a liquid sample are preferably removed.
As a means for removing bubbles from a liquid sample, a gas exchange membrane can be used. Examples of the gas exchange membrane include gas permeable membranes and membrane filters.
A gas permeable membrane has a cross-sectional structure schematically shown by reference numeral 31 in FIG. 6A. In such a gas permeable membrane, gaps between molecules of the material thereof are present in random orientations, and a gas component(s) permeates (permeate) the gas permeable membrane through the gaps. The gas permeation rate of the gas permeable membrane is low, but the gas permeable membrane does not allow a liquid to pass through it.
On the other hand, a membrane filter has a cross-sectional structure schematically shown by reference numeral 32 in FIG. 6B. As shown in FIG. 6B, a membrane filter 32 has a number of pores 33 penetrating therethrough. The pores 33 include those formed so as not to intersect one another and those intersecting one another. Irrespective of the type of pore 33, the diameter of the pores 33 is much larger than that (those) of a gas component(s) that should pass through the membrane filter. Therefore, the membrane filter has a gas permeation rate much higher than that of a gas permeable membrane because a gas component(s) can move in the membrane filter at a diffusion rate(s). However, in this case, only the surface tension of the membrane filter prevents a liquid from passing through the membrane filter, and therefore if a liquid sending pressure exceeds the surface tension, the liquid permeates the membrane filter 32 through the pores 33.
As a gas exchange apparatus for removing a gas component(s) from a liquid or transferring a gas component(s) to dissolve it (them) into a liquid, one utilizing hollow fiber membranes is used. Such hollow fiber membranes are used in the form of a module in which a number of hollow fiber membranes are tied in a bundle and caps are provided at both ends of the bundle. Such a module is used in such a manner that a liquid is allowed to flow through hollow fiber membranes and a gas contained in the liquid is removed by external aspiration or a gas is allowed to dissolve in a liquid in the hollow fiber membranes by the application of pressure to an external gas (see Patent Document 1).
An example of a total organic carbon measuring apparatus for measuring the total organic carbon of sample solution includes one including an organic matter oxidative decomposition unit for converting organic carbon to carbon dioxide; a carbon dioxide separation unit for extracting carbon dioxide generated in the organic matter oxidative decomposition unit into deionized water; and a detection unit for measuring the electrical conductivity of the deionized water discharged from the carbon dioxide separation unit to quantify carbon dioxide extracted at the carbon dioxide separation unit.
In the carbon dioxide separation unit of such a total organic carbon measuring apparatus, a gas permeable membrane is provided so as to separate sample solution having been subjected to oxidation in the organic matter oxidative decomposition unit from deionized water so that carbon dioxide contained in the sample solution is transferred into the deionized water through the gas permeable membrane.    Patent Document 1: Japanese Patent No. 3370407